Process for the production of alloys used as additive in the production of spheroidal graphite cast irons



D 1,' SHIRO TERADQ ETAL 3,544,

PROCESS FOR THE PRODUCTION OF ALLOYS USED AS ADDITIVE IN THE PRODUCTIONOF SPHEROIDAL GRAPHITE CAST IRONS Filed March 1, 1968 N0. 6MAGN/F/CAT/ON: /2ox United States Patent Office 3,544,310 Patented Dec.1, 1970 US. Cl. 75-129 2 Claims ABSTRACT OF THE DISCLOSURE A process forthe production of a ferrosilicon-base alloy adapted to be used in theproduction of spheroidal graphite cast irons as an additive, whichcomprises placing a slagmaking material in a ladle lined with a basicrefractory material, pouring a molten ferrosilicon from a ferrosiliconfurnace directly into said ladle, imparting a shaking motion to the meltin the ladle by eccentrically rotating said ladle and casting the meltinto a casting mold.

The present invention relates to a process for the production of aferrosilicon-base alloy adapted to be used in the production ofspheroidal graphite cast irons, which alloy is capable of formingspheroidal graphite in the cast iron more efliciently than thosedisclosed in Japanese patent publication No. 24,212/ 64, by thetreatment of a ferrosilicon of quality level substantially equal to thatof the commercially available ferrosilicons.

For producing spheroidal graphite cast iron most economically, a processhas been proposed in Japanese Patent No. 300,442, issued Oct. 13, 1962,which is characterized by subjecting a material iron to a silicontreatment using ferrosilicon-base alloys. However, not all offerrosilicons are adapted to be used for such a treatment. As suitableferrosilicon-base alloys, Japanese patent publication No. 24,212/64proposes those alloys which are composed of not more than 90% of ironand from 10 to 99% of silicon as being the basic components, added withnot more than 4% of calcium, not more than 10% of aluminum, the totalvalue of the percentage of calcium multiplied by 10 and the percentageof aluminum being not smaller than 3, not more than 0.05% of silicicacid or silicate and impurities which are inevitably introduced intosaid alloys.

The ferrosilicon-base alloys used in the process of aforesaid IapanesePat. No. 300,442 have heretofore been produced by charging lumps of acommercially available ferrosilicon in a magnesia-lined Heroult furnace,melting said ferrosilicon in said furnace with the addition of aslag-making material composed of quick lime, dolomite and fluorite,leaving the molten ferrosilicon to stand still, removing the slag andthereafter casting said molten ferrosilicon into a casting mold. Thespheroidal graphite cast iron produced with the ferrosilicon-base alloysobtained in the manner described has a tensile strength ranging from 50to 80 kilograms per square millimeter. However, the tensile strengthvaries largely from cast iron to cast iron and it has been extremelydifficult to produce a cast iron uniformly with a desired tensilestrength. Moreover, since the process is operated using a coldferrosilicon as a starting material, loss of silicon due to oxidationduring the melting operation has been great, the available percentage ofsilicon being only at highest.

In view of the above difliculties, the present inventors conductedvarious experiments with a view to obtaining an improved ferrosiliconalloy, by employing a process which comprises charging a moltenferrosilicon from a ferrosilicon furnace directly into a Heroultfurnace, instead of starting the process with a cold ferrosilicon,adding to said molten ferrosilicon the aforesaid slag-making material,after heating electrically leaving the melt to stand still, removing theslag and casting the melt into a casting mold. This method, however, wasfound impractical because the reaction proceeds at an unexpectedly slowand irregular speed and further the tensile strength of the cast ironsproduced with the use of thus obtained ferrosilicon alloys varies in awide range from 30 to 70 kilograms per square millimeter, although therewere the advantages that the power consumption for heating operation isreduced drastically and that the available percentage of silicon isimproved to as high as Upon reviewing the cause of failure met in theabovedescribed hot-charging method, it was concluded that the failurecould be attributed to unsatisfactory contact between the slag-makingmaterial and the molten ferrosilicon. Then, in order to produce asatisfactory contact between the slag-making material and the moltenferrosilicon, the present inventors further conducted the followingexperiment, in which the molten mixture of the ferrosilicon and theslag-making material was forcibly stirred in a fuel oil-heated ladle.

Namely, the slag-making material was charged in a ladle lined withmagnesia layer and heated until the surface of said magnesia lininglayer becomes red. Thereafter, a molten ferrosilicon from a ferrosiliconfurnace was directly poured into the ladle and immediately thereaftergreen wood was thrown into the melt in the ladle to effect bubbling ofthe gases generated. After allowing the melt to stand still and castingthe same, the ferrosilicon alloy obtained was tested, with the findingthat the tensile strengths of the spheroidal graphite cast ironsproduced with said ferrosilicon alloy were unexceptionally below 60kilograms per square millimeter, though the analyses of the metalcomposition and the slag composition after the process indicated that aconsiderably satisfactory contact had been effected between theslag-making material and the ferrosilicon.

As a result of this experiment, however, it has been acknowledged thatferrosilicon alloys of the type described could be produced economicallyby charging a molten ferrosilicon into a ladle and adding thereto aslag-making material. The only remaining problem to be solved was amanner in which the molten ferrosilicon alloy is stirred. The presentinventors have conducted further experiments and finally arrived at thepresent invention.

Namely, according to the present invention, there is provided a processfor the production of a ferrosilicon alloy adapted to be used in theproduction of spheroidal graphite cast irons, which comprises placing aslag-making material consisting primarily of quick lime or limestone ina ladle lined with a basic refractory material containing a minimumamount of silicon oxides, heating the ladle until the temperature of thelining surface is elevated to about .1,000 C., charging amoltenferrosilicon-base alloy into the ladle, maintaining the melt inthe ladle at a temperature not lower than 1,500 C., imparting to theladle an eccentric rotary motion to shake the melt in said ladle,stopping the shaking at a point at which the color of the spark from themelt has changed from red to bluish white while maintaining the melt ata temperature not lower than 1,350 C. and, after leaving the melt tostand still for a while, casting the melt into a casting mold. Theproduct obtained by the process described above fulfills therequirements for ferrosilicon alloys as set out in lapanese patentpublication No. 24,212/64 and further the cast irons produced by the useof the ferrosilicon alloy as an additive have a tensile strength of 60kilograms per square millimeter as cast, with minimum irregularity.Thus, it is possible, according to the process of the instant invention,to produce an excellent additive alloy which enable spheroidal graphitecast irons of high, uniform tensile strength to be produced.

The inventive process, which has been stemmed from the conventionalprocess using the Hroult furnace as described hereinbefore, ischaracterized in particular by effecting the stirring of the melt byshaking motion. The present invention has been achieved based on theresults of extensive industrial experiments. In order to obtain asatisfactory result according to the present invention, the process mustbe operated to fulfillthe following two conditions.

(1) LINING REFRACTORY MATERIAL The lining refractory material to be usedmust be selected from those basic refractory materials which containminimum amounts of silicon dioxide and alumina. In this view, it ispreferable to use magnesia and dolomite type refractory materials butnot preferable to use alumina bricks. The basicity ofthe refractorymaterial used for lining has a great bearing on the spheroidal graphiteforming capability of the product alloy, because use of carbonaceousmaterial will result in introduction of carbon, though in a smallamount, into the product alloy, with the result that the alloy tends todecay after casting, although there is no change in the spheroidalgraphiteforming capability. thereof, whereas when the basicity of theslag is acidic or weakly basic upon completion of the reaction, asatisfactory. spheroidal graphite-forming capability cannot be expectedof the alloy.

.The use of a basic refractory material, for instance, of magnesia type,however, will make it inevitable for the lining to react with silicon orfor the lining to act as a slag-making material. In order to avoiderosion of the lining, therefore, it is preferable touse as a liningmaterial magnesia bricks or the like which are unsusceptible to erosion,instead of castable materials which are susceptible to erosion.

(2) TEMPERATURE CONDITIONS' The temperature of the melt upon completionof the reaction must be not lower than 1,350 C. In the case of alloyswhose melting points are not lower than 1,350 C., the molten alloy aftercompletion of the reaction must be at a temperature not lower than saidmelting point and yet at a temperature at which the molten alloy has aconsiderable fluidity. The results of experiments have revealed that anadditive alloy having a desired spheroidal graphite-forming capabilitycannot be obtained at a temperature of the melt not, higher than 1,350C. The reaction between the slag-making material and theferrosiliconbase alloy in the present invention is an intenseendothermic reaction, so that the temperature of the molten alloy dropssharply during the reaction. Therefore, thetemperature of the moltenalloy of 1,350 C. or higher cannotbe obtained upon completion of thereaction, unless the' molten alloy is held at a temperature of not lowerthan 1,500 C. before the shaking operation. In this view, when a ladleof 1 ton or smaller in capacity is used and a molten alloy is to bepoured into the ladle at a temperature of 1,700 to 1,800 C. over aperiod of shorter than 10 minutes, it will be at least necessary to heatthe ladle beforehand by auxiliary heating means to a temperature ofabout 1,000 C. including the slag-making material placed therein.

The process of this invention has such economical advantages over theconventional process that the process can be accomplished in a veryshort period, that the available percentage of silicon can be improvedremarkably since silicon is not wastefully consumed by oxidation as hasbeen in the conventional process and that the power which has heretoforebeen required for heating a material alloy is not needed because of hotcharging. The inventive process is particularly advantageous in thatferrosilicon-base alloys which enable spheroidal graphite cast ironshaving a tensile strength of 60 kilograms per square millimeter orhigher to be produced, can be obtained on a stable basis and further inthat when the process is operated under the same conditions, variationin tensile strength value of the spheroidal graphite cast irons producedwith the product alloys can be minimized with respect to a desiredvalue, so that alloys capable of bringing about a desired tensilestrength in the spheroidal j graphite cast irons produced therewith canbe produced with a minimum percentage of rejection. In the past, thetensile strength of a spheroidal graphite cast iron has been assured byactually measuring the tensile strength on a sample piece which is takenfrom each tap. According to the process of this invention, such samplingis not required and the production can be controlled only by the controlchart. Consequently, the inspection costs can be saved substantially.

Now, the process of the present invention will be illustrated in detailby way of example with reference to the accompanying drawing which ismicroscopic photographs showing the structures of the spheroidalgraphite cast irons produced with the ferrosilicon-base alloys of thisinvention.

EXAMPLE The process of this invention was operated using a ladle whichhas a capacity of 500 kilograms (computed on pig iron) and is lined withmagnesia bricks. First of all, the surface of the lining was heated by afuel oil burner from one hour before the process. 15 minutes afterstarting the heating, a slag-making material was placed in the ladle andimmediately thereafter the combustion temperature of the fuel oil waselevated by mixing oxygen in the compressed air for the burnerto raisethe lining surface temperature. When the lining surface temperature hadreached a level higher than 1,000 C., a molten ferrosilicon was chargedinto theladle. The burner was put 011 when the amount of the moltenferrosilicon in the ladle reached a about 300 kilograms and a ladleshaking device was set in motion immediately to bodily rotate the ladlealong a horizontal circular path of millimeters in diameter at the rateof 92 revolutions per minute. The ladle was moved in the pathreciprocally in such a manner that it was rotated for 7 seconds in onedirection and, after having been held stationary for 1.5 seconds,rotated in an opposite direction for 7 seconds. In the meantime, thecolor of the spark scattering from the interior of the ladle along witha white smoke changed from red to bluish white and the motion of theladle was stopped at that point. The ladle was held still and, after'thesurface layer of the slag had been solidified, the ladle was inclinedand the melt was poured from the ladle into a casting mold through ahole bored through'the lower portion of the solidified slag.'The processdescribed above was repeated using differ'ent slagmaking materials indifferent amounts indi vidually, the results of which'are shown inthetable attached hereto;

Using the alloys thus produced, spheroidal graphite cast irons wereproduced and the tensile strengths of the individual spheroidal graphitecast irons were measured, in the manner described below: 1

Namely, in a basic arc furnace of a capacity of 50 kilowithout shakingthe ladle, which were generated intensely upon throwing green wood intothe molten metal. In these cases, the tensile strengths of the productcast irons are not higher than 60 kilograms per square millimeter, thatis lower than those of the cast irons in the other runs.

grams was charged 50 kilograms of scrap steel and molten This factproves the necessity of the shaking operation. therein with the additionof carbon in such an amount that The experiments of Run Nos. 3 and 4 inCategory II are the carbon content in the melt, after removing the slag,the repersentatives of many experiments by which it has would wall inthe range from 3.8 to 4%. The melt was been established that a tensilestrength of cast iron of 60 added with a basic flux for reduction andrefining, and kilograms per square millimeter or higher cannot beexthereafter with 800 grams of a ferrosilicon alloy to be testpectedwhen the temperature of the molten metal upon ed. The resultant moltenmetal was cast in the temperature completion of the shaking operation isnot higher than range from 1,470 to l,500 C. The molten metal was also1,350 C. The structures of the spheroidal graphite cast poured in aseparate ladle in an amount of 10 kilograms irons obtained from Run Nos.1 and 6 are shown in the and, after adding thereto 300 grams offerrosilicon alloy attached microscopic photographs at a magnificationof to be tested, the molten metal was immediately cast into 120 times.

Analysis of molten metal, percent s1 Ca Al Run Before After Before AfterBefore After Category No treatment treatment treatment treatmenttreatment treatment I 1 68. 7 67. 4 0. 11 1. 22 0. 22 0. 65 2 71.0 68.80. 44 1. 34 0. 44 0. 72 H 3 72. 9 70. 6 1. 10 1. 45 0. 39 2. 21 4 67. 268. 5 0. 88 1. 36 0. 64 1. 96 m 5 64. 5 64. 4 0. 0s 0. 88 0. 40 1. 4s 669. 1 69. 1 1. 02 1. 31 0. 77 1. 74 Iv 7 70. 2 71. 4 0. 32 1. 52 0. s20. 9s s 71. s 71.4 0. 31 0. 55 0. 0. 5s 9 71. s 71.0 0. 3s 0. 52 0. 670. 59 V 10 69. 7 66. 7 1. 15 1. 48 0. 49 0. 90 11 68. 7 67. 4 1. 43 1.48 0. 74 0. 96 VI 12 71. 2 69. 6 1. 01 1. 23 0. 6s 1. 34 13 69. 3 67. 50. s7 1. 96 0.67 1. 87 VII 14 98.5 97. 5 o. 15 0. 90 0. 1o 0. 53 15 9s.2 97. 2 0. 20 1. 02 0. 0s 0. 61

Composition, kg.

Molten metal Slag-making material temperature, C. Shaking Tensile RunQuick period, Before After strength Category No Metal lime AluminaFluorite min. treatment treatment kg./n1rn.

1 Carbon powder 2. 2 Limestone 20. Norris:

a keel block of 40 millimeters in wall thickness to produce a test pieceof Japanese Industrial Standards No. 4 type, on which the tensilestrength of the spheroidal graphite cast iron was measured.

In the table, the experiments in Categories I to VI inclusive wereconducted with a ferrosilicon containing about of silicon and those inCategory VII were conducted with metallic silicon containing about 98%of silicon. The experiments in Category VI were conduct- What is claimedis:

1. A process for the production of a ferrosilicon consisting essentiallyof iron and silicon and adapted to be used in the production of aspheroidal graphite cast iron as an additive, comprising placing aslag-making material composed primarily of quick lime or limestone in aladle lined with a basic refractory material containing a minimum amountof silicon oxides, heating the ladle until the temperature of the liningsurface is elevated to ed by forcibly stirring the molten metal by meansof gases, about 1,000 C., charging a molten ferrosilicon into the ladle,maintaining the molten metal in the ladle at a temperature not lowerthan 1,500 O, imparting a shaking motion to the molten metal in theladle by eccentrically rotating said ladle, continuing the shakingoperation until the reaction has been completed while maintaining thetemperature of the molten metal at such level that said molten metalwill beat a temperature of not lower than 1,350 C. upon completion ofthe reaction and casting said molten metal into a casting mold.

2. A process in accordance with claim 1 wherein said ladle lining ofbasic refractory material is formed of erosion resistant magnesiabricks.

References Cited UNITED STATES PATENTS L. DEWAYNE RUTLEDGE, PrimaryExaminer 10 J. E. LEGRU, Assistant Examiner US. Cl. X.R.

